Design of new strategy for green algal photo-hydrogen production: Spectral-selective photosystem I activation and photosystem II deactivation

A new strategy in photosynthetic hydrogen (photo-H₂) production from green algae was developed based on theory and successfully demonstrated. The new strategy applied a spectral-selective photosystem I (PSI) activating/photosystem II (PSII) deactivating radiation (or PSI light) that would drive a steady flow of electrons in the electron transport chain for delivery to hydrogenase for photo-H₂ production, but would reduce oxygen production through water photolysis below the respiratory oxygen consumption so that an anoxic condition would be maintained as required by hydrogenase. Implementing the strategy by using a PSI light (692nm peak, 680-700nm) on Chlamydomonas reinhardtii cells resulted in relatively sustained photo-H₂ production (total of 0.108mLH₂mg^-1Chl, exceeding 0.066mLH₂mg^-1Chl under white light). The strategy also proved successful and convenient in allowing cells to alternately switch between photo-H₂ production and a recovery period by simply turning on or off the PSI light.